Apparatus and method for steering a vehicle

ABSTRACT

A steering system for a vehicle includes a load displacement system allowing transient loads of the steering mechanism to be displaced. The steering system also includes a first coupling mechanism coupling an electric motor to a rack housing, and a second coupling mechanism coupling a ball nut to a rack and method.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a divisional application of U.S. application Ser. No.11/016,039, filed Dec. 17, 2004, which is a continuation-in-part of U.S.patent application Ser. No. 10/765,731, filed Jan. 26, 2004, which is acontinuation application of U.S. patent application Ser. No. 10/262,751,filed Oct. 1, 2002, (now U.S. Pat. No. 6,705,423), which is a divisionalof U.S. patent application Ser. No. 09/920,181, filed Aug. 1, 2001 (nowU.S. Pat. No. 6,488,115), which is related to U.S. patent applicationSer. No. 09/664,850, filed Sep. 19, 2000, wherein the contents of all ofthe above listed applications and patents are incorporated in theirentirety herein by reference.

This application also claims priority to U.S. Provisional PatentApplication 60/540,643 filed on Jan. 30, 2004, wherein the contents areincorporated in its entirety herein by reference.

This application is also related to U.S. patent application Ser. No.09/650,869, filed Aug. 30, 2000, the contents of which are incorporatedherein by reference thereto.

This application is also related to U.S. patent application Ser. No.09/663,549, filed Sep. 18, 2000, the contents of which are incorporatedherein by reference thereto.

FIELD OF THE INVENTION

This invention is related generally to steering systems, and, moreparticularly, this invention is related to an interface between a rotaryto linear actuator and a linear section of the steering system

BACKGROUND OF THE INVENTION

Some current steering system designs have replaced the hydraulic powersteering pump with electrically assisted systems based on fuel economy,modularity, engine independence, and environmental issues.

With electrically actuated or electrically assisted steering systemsthere is a significant servo mechanism design challenge associated withthe need to maintain proper kinematical constraint, while at the sametime, providing reasonable insulation from the drawbacks of tolerancestack up which may produce system lock up.

Although a successful servo mechanism design may appear to be acombination of basic “catalogue” mechanisms (e.g. ball-screw, gears,belts, various joints, etc.), the way these are used in combinationrepresents an unmistakably cardinal feature of this art.

The current state of engineering meets these concerns by anticipatingthe stresses likely to be encountered by designing heavy-dutycomponents. Needless to say, these designs are expensive to manufacture,have excessive performance challenges because of the increased inertiaand friction, and add to the overall weight of the vehicle.

In most steering applications development of the actuator for powerassist follows the synthesis and design of the suspension and steeringlinkages. Steering linkages could be steering the front wheels or rearwheels or both. Thus power assist steering may take the form ofassisting front steering mechanism, rear steering mechanism or both. Thesteering linkage could also be connected to the steering wheelmechanically or via electronics that follow certain logic such as in“steer-by-wire” applications.

BRIEF SUMMARY OF THE INVENTION

In one exemplary embodiment, a steering system for a vehicle may includea steering wheel being positioned for manipulation by a vehicleoperator, a steering mechanism for transmitting a steering operation ofthe steering wheel to vary the angular configuration of at least onewheel of the vehicle, a power assist mechanism for providing anassisting force to the steering mechanism, the power assist mechanismbeing activated in response to the steering operation of the steeringwheel and a load displacement system being operatively coupled to thepower assist mechanism, the load displacement system allowing transientloads of the steering mechanism to be displaced.

In another exemplary embodiment, a steering system for a vehicleincludes a rack being movably mounted within a rack housing, the rackbeing coupled to a steerable road wheel, a ball-screw mechanism beingcoupled to the rack at one end and an electric motor at the other, theelectric motor providing an actuating force to the ball-screw mechanism,the actuating force causing the rack to move linearly within the rackhousing, a first coupling mechanism coupling the electric motor to therack housing, and a second coupling mechanism coupling the ball nut tosaid rack.

In another exemplary embodiment, a method for providing an actuationforce to a rack of a vehicle, includes isolating non-axial loads from anelectric motor of a steering system, the motor providing a rotationalforce to a rotatable member of a rotary-to-linear conversion device, andisolating non-axial loads from a linearly actuatable member of saidrotary-to-linear conversion device, the linearly actuatable member beingcoupled to a rack of said steering system.

In yet another exemplary embodiment, a steering system for a vehicleincludes a rack being movably mounted within a rack housing, the rackbeing coupled to a steerable road wheel, a rotary-to-linear mechanismbeing coupled to the rack at one end and an electric motor at the other,the electric motor providing an actuating force to the rotary-to-linearmechanism, the actuating force causing the rack to move linearly withinthe rack housing, a first coupling mechanism coupling the electric motorto the rack housing, and a second coupling mechanism coupling the ballnut to the rack.

In another exemplary embodiment, an actuator for a steering system, mayinclude a rotary to linear actuator, a movable linear section, and aninterface between the rotary to linear actuator and the linear section,wherein the interface is limited to three degrees of freedom and theactuator is limited to one degree of freedom.

In another exemplary embodiment, an interface for an actuator may adjoina movable linear section and a rotary to linear actuator, and theinterface may comprise a block on a plane joint.

Other systems and methods according to embodiments will be or becomeapparent to one with skill in the art upon review of the followingdrawings and detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an illustration of a steering system for a vehicle;

FIG. 2 is an illustration of a portion of the steering system in FIG. 1;

FIG. 3 is a perspective view of exemplary embodiments of arack-independent actuator;

FIG. 4 is a cross-sectional view of exemplary embodiments of arack-independent actuator;

FIG. 5 is another perspective view of a rack-independent actuator;

FIG. 6 is an end view of exemplary embodiments of a rack-independentactuator;

FIG. 7 is a top plan view of exemplary embodiments of a rack-independentactuator;

FIGS. 8 and 9 are perspective views of a rack-independent actuatorillustrating the universal joints in an exploded view;

FIG. 10 is an end perspective view of exemplary embodiments of therack-independent actuator;

FIG. 11 is a partial cross sectional perspective view of exemplaryembodiments of a rack-independent actuator;

FIG. 12 is a partial cross sectional perspective view of exemplaryembodiments of a universal joint of a rack-independent actuator;

FIG. 13 is a partial cross sectional perspective view of exemplaryembodiments of a rack-independent actuator;

FIG. 14 is a partial cross sectional perspective view of exemplaryembodiments of a universal joint of a rack-independent actuator;

FIG. 15 is a block diagram of a rack-independent actuator system;

FIG. 16 a diagrammatic view of a steer by wire system;

FIG. 17 is a diagrammatic view of a steer by wire system withindependent actuators for each steerable wheel of a vehicle;

FIG. 18 is a diagrammatic front view of an interface location between arotary to linear actuator and a linear section of an actuator;

FIG. 19 is a diagrammatic front view of a collinear load acting on aballscrew-screw;

FIGS. 20 and 21 are cross-sectional views of a system incorporating theconcepts of FIG. 19;

FIG. 22 is a perspective view of the special case actuator of FIG. 19;

FIG. 23 is a perspective view of the interface of FIG. 19 with respectto a ball screw nut and a rack;

FIG. 24 is a perspective view of an overall appearance of a special caseactuator shown in FIG. 22;

FIG. 25 is a diagrammatic front view of an alternate interface between arotary to linear actuator and a linear section of an actuator;

FIG. 26 is a perspective view of an actuator incorporating the mechanismof FIG. 25;

FIGS. 27-29 are cross-sectional views of the actuator of FIG. 26;

FIG. 30 is an enlarged detail showing a ballscrew nut and a plane;

FIG. 31 is a cross-sectional view of an alternate embodiment of theactuator of FIG. 26;

FIG. 32 is a cross-sectional view of the actuator of FIG. 26;

FIG. 33 is a perspective view of an interface between a rotary to linearactuator and a linear section;

FIG. 34 is a perspective view of an alternate interface between a rotaryto linear actuator and a linear section; and,

FIG. 35 is a perspective view of another alternate interface between arotary to linear actuator and a linear section.

DETAILED DESCRIPTION OF THE INVENTION

Aspects of these embodiments relate generally to an apparatus and methodfor steering a vehicle, and more specifically to a rack-independentactuator. A steering system for a vehicle may include a rack-independentactuator. The rack-independent actuator may include component parts thatisolate from undesirable loads by two universal joints that may isolatemechanical components of the actuator from transient loads that may beencountered by the rack or rack housing.

The system may be powered by a rotary type electric motor. The motor hasspeed reducers and rotary-to-linear actuators to achieve feasible sizeand linear actuation. The actuation unit is decoupled from thedirectionally unwanted loads by providing universal joints (or anequivalent degree of freedoms) at either end. One universal joint ismounted to the housing that holds the motor rotary-to-rotary speedreducer and the movable shaft of the linear-to-rotary actuator, and theother is mounted to a member that is linearly moved by thelinear-to-rotary actuator.

The use of universal joints (or gimbals), which provides kinematicaldegrees of freedom to prevent non-axial loads, also prevents bendingmoments on the rotary-to-linear actuator. In particular, such loads mayresult from the misalignment of the shafts and/or non-axial loading fromother components. This situation may produce undesirable friction andhigh stresses resulting in loss of efficiency and/or undesirablesteering feel. By avoiding the non-axial loads, the mechanizationbecomes feasible for all types of linear-to-rotary mechanizations, whichtoday are limited to very special ball-screws.

Exemplary embodiments of the independent actuator system of employ thejudicious use of universal joints, (gimbal) expansion joints, or otherequivalents to achieve freedom from lock-up as well as compensation forreasonable tolerance stack-up errors, which must be designed aroundcurrent steering system designs.

A benefit of the Electric Power Steering and Steer-by-Wire system is theenhanced comfort to the driver of a vehicle equipped with this system.The driver of such a vehicle would experience improved handling overless-than-smooth terrains e.g., potholes, graded surfaces, etc.

Less-than-smooth terrain increases the loads and deflections encounteredby the steering system. Thus, any bumps experienced by the vehicle mayincrease the wear and tear to the steering system, thus shortening andreducing its effective life.

Referring now to FIGS. 1 and 2, a steering system 10 for use in avehicle 12 (not shown) is illustrated. Steering system 10 allows theoperator of vehicle 12 to control the direction of vehicle 12 throughthe manipulation of steering system 10.

A steering column 14 provides mechanical manipulation of the vehicle'swheels in order to control the direction of the vehicle. Steering column14 includes a hand wheel 16. Hand wheel 16 is positioned so that a usercan apply a rotational force to steering column 14. An upper steeringcolumn shaft 18 is secured to hand wheel 16 at one end and columnuniversal joint 20 at the other. Column universal joint 20 couples uppersteering column shaft 18 to a lower steering column shaft 22. Lowersteering column shaft 22 is secured to column universal joint 20 at oneend and a gear housing 24 at the other. Gear housing 24 includes apinion gear 26 (FIG. 2). Pinion gear 26 of gear housing 24 is positionedto make contact with a matching toothed portion 28 of a rack assembly30. Pinion gear 26 has helical teeth that are meshingly engaged withstraight-cut teeth of matching toothed portion 28.

The pinion gear, in combination with the straight-cut gear teeth of therack, form a rack and pinion gear set. The rack 45 is coupled to thevehicle's steerable wheels with steering linkage in a known manner.

Tie rods (only one shown) 32 are secured to rack assembly 30 at one endand knuckles 34 (only one shown) at the other.

As a rotational force is applied to steering column 14, through themanipulation of hand wheel 16 or other applied force, the pinion gear ofgear housing 24 is accordingly rotated. The movement of the pinion gearcauses the movement of rack assembly 30 in the direction of arrows 36,which in turn manipulates tie rods 32 and knuckles 34 in order toreposition wheels 36 (only one shown) of the motor vehicle. Accordingly,when the steering wheel 16 is turned, rack 45 and pinion gear 26 convertthe rotary motion of the steering wheel 16 into the linear motion ofrack 45.

In order to assist the user-applied force to the steering system, anelectric motor 38 is energized to provide power assist to the movementof rack 45, aiding in the steering of the vehicle by the vehicleoperator.

Electric motor 38 provides a torque force to a motor pulley 40 via motorshaft 42. The rotation force of motor pulley 40 is transferred to a belt44. There are retaining walls 41 on either one of the pulleys 40 and/orball-screw pulley 62 to help prevent belt 44 from slipping completelyoff. Alternatively, motor pulley 40 can be configured to have noretaining walls. In yet another alternative, belt 44 is replaced by achain or gear system or any rotary to rotary drives that provides arotational force to the screw 64 of the ball-screw mechanism.

Accordingly, and as a torque force is applied to the belt 44, therotational force is converted into a linear force via therotary-to-linear actuator (ball-screw assembly 66), and rack 45 is movedin one of the directions of arrows 36. Of course, the direction ofmovement of rack assembly 30 corresponds to the rotational direction ofmotor pulley 40. Belt 44 has an outer surface 46 and an inner engagementsurface 48. The configuration belt 44 and the position of electric motor38 allows inner engagement surface 48 of belt 44 to wrap around andengage both the motor pulley 40 and ball-screw pulley 62, that are fixedto the rotary portion of a ball-screw 66 (rotary to linear actuator)mechanism.

Electric motor 38 is actuated by a controller 52 that receives inputsfrom a torque sensor 54 and a rotational position sensor 56. Sensor 56provides a steer angle signal to controller 52.

In addition, and as the motor shaft 42 of electric motor 38 turns, themotor shaft position signals of each phase are generated within electricmotor 38 and are inputted into controller 52 through a bus 58.

Controller 52 also receives an input in the form of a vehicle speedsignal. Accordingly, and in response to the following inputs: vehiclevelocity input; operator torque input (sensor 54); steering pinion gearangle (sensor 56); and motor shaft 42 position signals (bus 58),controller 52 determines the desired electric motor's current phases andprovides such currents through a bus 60.

Motor pulley 40 is rotated by motor shaft 42 of electric motor 38. Asecond pulley 62 is fixedly secured to the ball-screw 64 screw (or therotary part of a rotary to linear actuator) of a ball-screw assembly 66.The ball-screw assembly 66 converts the rotary force of belt 44 into thelinear movement of a ball nut 68.

Motor pulley 40 and ball-screw pulley 62 may be constructed out of alightweight material such as aluminum or composites. This allows theoverall mass and inertia of steering system to be reduced in order toimprove manufacturing costs and performance, as well as vehicle fuelefficiency.

FIGS. 1 and 2 illustrate a power assist steering system that includes amechanical connection between (rack and pinion) hand wheel 16 and rackassembly 30.

Alternatively, and in applications in which a “steer-by-wire system” isemployed, there is no direct mechanical connection between hand wheel 16and rack assembly 30. In this application, the driver's rotationalmovement of the hand wheel 16 (and /or signal from an equivalent drivercontrol device such as a joystick, pedal(s) and other mechanism formanipulation by the vehicle operator) is input into the controller 52while electric motor 38 provides the necessary force to manipulate rackassembly 30.

Referring now to FIGS. 3-14, a rack-independent actuator 70 isillustrated. In accordance with an exemplary embodiment,rack-independent actuator 70 provides the necessary force to effect thelinear movement of a rack 45 coupled to the steerable wheels of avehicle. Rack-independent actuator 70 performs the functions of rotatingthe steerable wheels of a vehicle in response to an input such as drivermanipulation of a steering wheel. In addition, and while performing thisfunction the rack independent actuator 70 isolates its reductionmechanisms and/or conversion mechanisms necessary to effect the rotationof the steerable wheels from transient and non-axial (to the rack) loadsby a pair of universal joints 72 and 74.

Rack-independent actuator 70 is also contemplated for use with a powerassist steering system (FIGS. 1 and 2) and/or a “steer-by-wire system”(FIGS. 16 and 17) and/or rear wheel steering and/or four-wheel steering.

FIGS. 8 and 9 illustrate universal joints 72 and 74 in an exploded viewin order to illustrate the component parts of the same.

Universal joint 72 secures a housing 75 to a mounting member 76 of rackassembly 30. Universal joint 72 contains two sets of hinge pins, orpivots 78 and 80, the axis of each set being perpendicular to the other.Each set of pins is connected to the other by a central gimbal ring 82.

As an alternative, universal joints 72 and 74 may be replaced by acompliant member that allows similar degrees of freedom for the range ofmotion necessary to isolate the reduction mechanisms from transient andnon-axial (to the rack) loads. For example, gimbal ring 82 is replacedby a rubber ring that is inserted into mounting member 76 while alsocovering a portion of housing 75. The rubber ring is compressible andthus capable of providing kinematic freedom. Similarly, gimbal ring 92may be replaced by a compliant rubber ring.

In yet another alternative, rack independent actuator may be constructedwith a universal joint and a rubber compliant member. For example,universal joints 72 and a rubber compliant member replacing universaljoint 74 or vice versa.

In an exemplary embodiment, pins 78 and 80 are pressed at theirrespective openings in gimbal ring 82. This allows the rotationalmovement of gimbal ring 82 while also providing a means for securing thesame. Alternatively, pins 78 and 80 slip in openings in housing 75 andmounting member 76.

Alternatively, pins 78 and 80 and their respective openings in gimbalring 82, housing 75 and mounting member 76 are configured to provide amovable means of securing the same.

Pins 78 movably connect gimbal ring 82 to housing 75. In an exemplaryembodiment, housing 75 is configured to have an elongated cylindricalshape allowing a portion of housing 75 to be inserted within an inneropening of gimbal ring 82. Thus, pins 78 allow gimbal ring to be movablysecured to housing 75.

In addition, pins 80 movably connect gimbal ring 82 to mounting member76. Mounting member 76 is fixedly secured to an outer housing 77 of rackassembly 30. In an exemplary embodiment, mounting member 76 defines aninner opening 88 sufficiently large enough to pass over gimbal ring 82.

Accordingly, gimbal ring 82 is movably secured to housing 75, andhousing 75 is sufficiently long enough to position gimbal ring 82 withinopening 88 of securement member 76, thus gimbal ring 82 connects housing75 and securement member 76 by pins 78 and 80. Pins 78 pass throughopenings 73 in securement member 76 and movably secured gimbal ring 82to securement member 76, while pins 80 movably secure gimbal ring 82 tohousing 75 by engaging openings 81 in housing 75. In an exemplaryembodiment, pins 78 and 80 are positioned at right angles with respectto each other. Of course, the angular positioning of pins 78 and 80 mayvary as long as the intended effect of isolating potions of the rackindependent actuator from unwanted loads is achieved.

For example, pins 80 prevent a load from being transferred in-betweenmounting member 76 and gimbal ring 82 in a first direction while pins 78prevent a load from being transferred in-between housing 75 and gimbalring 82 in a second direction. The first and second directions beingdifferent from each other.

As an alternative, and in order to prevent a load from being transferredto gimbal ring 82 and/or gimbal ring 92, the pins that secure the gimbalrings are covered with plastic and/or rubber to further enhance theisolation of the mechanism from unwanted loads.

Rack-independent actuator 70 has an electric motor assembly 90. Electricmotor assembly 90 includes electric motor 38, rotatable shaft 42, andmotor pulley 40 that is fixedly secured to motor shaft 42. As pulley 40is rotated by motor shaft 42, belt 44 engages with pulley 40 as well aspulley 62. Since pulley 62 is fixedly secured to screw 64 of theball-screw mechanism, the rotational movement of pulley 62 causes screw64 of the ball-screw mechanism to rotate. Accordingly, motor 38, belt44, pulleys 40 and 62 provide a rotary to rotary conversion, which isdetermined by the dimensions of pulley 40 and 62 with respect to eachother (e.g. gear ratio).

As an alternative and in accordance with the exemplary embodiments, itis contemplated that other mechanisms and means for rotary to rotaryconversion may be employed with the exemplary embodiments. For example,pulleys 40 and 62 and belt 44 can be replaced by a direct mechanicallinkage such as a gear train rotary to rotary drive or equivalentthereof.

One end of screw 64 of the ball-screw mechanism is mounted for rotationwithin a plurality of bearings 65 located within housing 75 proximate topulley 62. A pre-load nut adjuster or locking nut 67 screws onto thescrew 64 of the ball-screw mechanism adjacent to bearings 65, once inposition locking nut is secured to screw 64 of the ball-screw mechanismthrough the use of a plurality of locking screws 63 which when rotatedlock locking nut 67 onto screw 64 of the ball-screw mechanism. Thus,bearings 65 are positioned between locking nut 67 and pulley 62 allowingfor the rotational movement of screw 64 of the ball-screw mechanism. Theother end of screw 64 of the ball-screw mechanism is rotatably supportedby ball-screw nut 68 of ball-screw mechanism 66. Accordingly, therotational movement of screw 64 of the ball-screw mechanism by motor 38is isolated at one end by universal joint 72.

A portion of screw 64 of the ball-screw mechanism passes throughball-screw nut 68, and the respective surfaces of screw 64 of theball-screw mechanism and ball-screw nut 68 are configured to effect thelinear movement of ball-screw nut 68 as screw 64 of the ball-screwmechanism is rotated. In an exemplary embodiment, a plurality of balls69 are received within a pair of threaded or grooved surfaces 71positioned on the inner surface of ball-screw nut 68 and the outersurface of screw 64 of the ball-screw mechanism. The interface of screw64 of the ball-screw mechanism and ball-screw nut 68 of ball-screwmechanism 66 are constructed in a known manner.

Accordingly, and as screw 64 of the ball-screw mechanism is rotated bythe rotational movement of pulley 62 by motor 38, the rotationalmovement of screw 64 of the ball-screw mechanism is converted intolinear movement of ball-screw nut 68. It is here that rotary to linearconversion occurs. As an alternative, other means for rotary to linearconversion are contemplated for use with the exemplary embodiments.

The interface between ball-screw nut 68 and rack 45 is isolated byuniversal joint 74. Ball-screw nut 68 is secured to a gimbal ring 92 ofuniversal joint 74. Similarly to universal joint 72, universal joint 74contains two sets of hinge pins or pivots 94 and 96, the axis of eachset being perpendicular to the other. Each set of pins is connected tothe other by central gimbal ring 92.

In an exemplary embodiment, pins 94 and 96 are pressed in theirrespective openings in gimbal ring 92. This allows the rotationalmovement of gimbal ring 92 while also providing a means for securing thesame.

Alternatively, pins 94 and 96 and their respective openings in gimbalring 92, ball-screw nut 68 and housing member 100 are configured toprovide a movable means of securing the same.

Pins 94 movably connect gimbal ring 92 to ball-screw nut 68 allowing formovement in a first direction. In an exemplary embodiment, gimbal ring92 is configured to have a cylindrical shape slightly larger thanball-screw nut 68, allowing a portion of ball-screw nut 68 to beinserted within gimbal ring 92. Pins 94 are received within a pair ofpin openings 98 in the ball-screw nut 68. It is noted that universaljoint 74 and ball-screw nut 68 are shown in FIGS. 8 and 9 in an explodedmanner so as to illustrate the attachment of universal joints 72 and 74.

Pins 96 movably connect gimbal ring 92 to a housing member 100 allowingfor movement in second direction, the second directional plane beingorthogonal to the first directional plane. Pins 96 pass through a pairof apertures 102 in housing 100, thus movably connecting gimbal ring 92to housing 100.

The gimbal mechanisms or in particular universal joints 72 and 74provide the necessary kinematic degrees of freedom to prevent non-axialloads and for turning or bending moments on the ball-screw nut or screw,such as those that would result from misalignment of the shafts, fromproducing undesirable friction and the resultant loss of efficiency onthe rotary to linear motion conversion mechanism.

In so doing, the torque output and power consumption requirements of themechanism used to turn the ball-screw such as the electric motor isreduced. This allows the electric motor to be reduced in size as well asthe components of the rotary to linear actuator. This is particularlyuseful for applications such as vehicular electric steering actuators,where the dynamic loads experienced by the vehicle and the requirementsplaced on the mechanism can significantly impact the motor and actuatormechanism requirements. The reduction in power consumption of the motorand the weight reductions associated with a smaller electric motor andmechanism represent desirable to design parameters.

Referring now in particular to FIG. 4, housing 100 is fixedly secured torack 45 through a plurality of bolts 104 which pass throughcomplementary bolt openings 106 in rack 45 and housing 100. Accordingly,and as a rotational force is applied to screw 64 of the ball-screwmechanism, ball-screw assembly 66 converts the rotary movement of screw64 of the ball-screw mechanism into the linear movement of ball-screwnut 68. Ball-screw nut 68 is connected to rack 45 through a universaljoint 74, which is connected to ball-screw nut 68 at one end and housing100 at the other. Housing 100 is fixedly secured to rack 45 andaccordingly, as ball-screw nut 68 moves in the direction indicated byarrows 36, a similar movement of rack 45 is produced.

Housing member 100 is configured to have a mounting portion 101 that isconfigured to be received within opening 108. Mounting portion 101 isconfigured to be slidably received within opening 108 and contains theapertures into which bolts 104 are received.

Universal joints 72 and 74 isolate electric motor assembly 90 andball-screw pulley 62 from transient non-axial loads, which may damage ormisalign pulleys 40 and 62. Moreover, universal joints 72 and 74 isolatethe system from undesirable loads or stack buildup that may be theresult of misalignment of a component part such as rack 45, ball-screw64 and/or any other component part that may produce an undesirable loador stack buildup.

The rack-independent actuator also allows the two pulleys on the beltand pulley mechanism to be mounted to the same housing and to eliminateall force components that could alter their parallelism.

Moreover, the rack-independent actuator of an exemplary embodiment nolonger requires the motor shaft of motor 38 or the screw 64 of theball-screw mechanism to be parallel to rack 45, as motor assembly 90 andscrew 64 of the ball-screw mechanism are isolated from rack 45 throughthe use of universal joints 72 and 74. Thus, any misalignment of screw64 of the ball-screw mechanism with regard to rack 45 is accommodatedfor by universal joints 72 and 74. Accordingly, motor shaft 42 need onlybe parallel to screw 64 of the ball-screw mechanism, or alternatively,pulleys 40 and 62 need only be parallel to each other. Accordingly, andsince they are mounted to the same housing, this is easily achieved andmaintained. Moreover, any loads that may cause misalignment are isolatedfrom the motor assembly through the use of universal joints 72 and 74.

Also, pulleys 40 and 62 may be configured with or without retainingwalls because, as stated above, belt 44 is isolated from transientforces, thus reducing belt/pulley production costs, since the belt andpulley system does not have to be designed to withstand large forces.

Referring back now to FIGS. 4, 8, 9 and 11-14, outer housing 77 of rackassembly 30 is configured to have an elongated opening 108. In order toprevent the rotational motion of the rack 45, an anti-rotation device110 is secured to rack 45 (FIG. 4) that moves within the confinement ofthe elongated opening 108.

In an exemplary embodiment, anti-rotation device 110 is a plug 112fixedly secured within an opening 114 of rack 45. Plug 112 has an uppermember depending outwardly from rack 45, and is sized and configured topass along in elongated opening 108. In addition, and in order to reduceany frictional buildup between plug 112 and the elongated opening 108, aplurality of bearings 116 are positioned around the periphery ofanti-rotation device 110. Accordingly, anti-rotation device 110 preventsrotational movement of rack 45 while allowing linear movement of thesame.

Rack assembly 30 is also configured to have a pair of mounting members118. Mounting members 118 are configured to secure rack-independentactuator 70 to a vehicle frame (not shown).

In addition, and referring now to FIG. 4, housing 77 of rack assembly 30has a pair of apertures 120. Apertures 120 are positioned to allow atool such as a screwdriver or other type of tool to be inserted intoopenings 120 in order to facilitate the securement of bolts 104 tohousing 100 and rack 45.

The steering system is equipped with several sensors that relayinformation to the electric motor 38 by way of a controller 52 (FIG. 1).Controller 52 will track the position and force upon rack 45 at alltimes by means of a pair of force sensors 122. Force sensors 122 provideinput into controller 52 corresponding to the amount of force includedat the ends of rack 45.

A pair of absolute position sensors 124 and a high-resolution sensor 126also provide input into controller 52 in the form of a rack positionlocation. For example, an on-center position sensor may compriseHall-Effect devices, which are mounted within rack-independent actuator70. It may be understood that the sensors and controller 52 comprise acalibration means for maintaining the values of the steering positionsignals that correspond with the actual steering positions.

Rack 45 has a center position in which the steerable wheels of a vehicleare directed straight ahead relative to the vehicle. In an exemplaryembodiment, rack-independent actuator 70 will provide a return torquethat assists in returning the steering system to a center position.

In this system, the return torque is generated by electric motor 38, anda return torque component of the total desired torque signal isgenerated in controller 52 based upon the input received from sensors122, 124, and 126. Thus, an accurate signal of the steering position isderived from absolute position sensor 124.

In order to express the full range of steering angles as the output ofabsolute position sensor changes, the apparatus utilizes an algorithm incontroller 52. The algorithm may be embodied in a programmed digitalcomputer or a custom digital processor (not shown).

Referring now to FIG. 15, a block diagram illustrates the use of theuniversal joints and the unit interaction between various components ofthe rack-independent actuator system.

Block 130 represents the electric motor. Block 130 interfaces with block132 that represents the rotary-to-rotary assembly of therack-independent actuator system. Block 130 also interfaces with thehousing of the ball-screw indicated at block 134. Block 132 interfaceswith a block 136 that represents a rotary-to-linear assembly. Block 136interfaces with a block 138 that represents the bearings of theball-screw, and block 138 interfaces with the ball-screw housing. Block140 represents a high-resolution sensor that interfaces with the housing(block 134) and the rotary to linear assembly (block 136).

Block 142 represents an interface between the rotary-to-linear assemblyand the housing of the rack assembly.

Block 144 represents the housing of the rack assembly. Block 146represents an absolute position sensor that interfaces with box 136 andbox 144. Block 148 represents a tie rod and force sensor that interfaceswith the housing of the rack assembly (block 144).

Block 150 represents the interface between housing 134 and the rackhousing 144. It is here at block 150 in which universal joint 72 orstationary universal joint 72 is inserted to isolate the motor and beltand pulley assembly from the housing of the rack assembly.

Block 142 represents the interface between the rotary-to-linear assemblyhousing and the rack assembly. It is here at block 142 in whichuniversal joint 74 or mobile universal joint 74 is inserted to isolatethe movement of the rack assembly from the ball-screw nut of theball-screw assembly.

This system accomplishes compensation through a series of sensors thatprovide feedback to several components. For instance, therotary-to-linear assembly at block 136 receives inputs from the absoluteposition sensors at block 146. In this embodiment, the absolute positionsensors are mounted to the ball-screw assembly. The absolute positionsensor at block 146 provides steer angle signals that are sent to thecontroller.

While exemplary embodiments have been described with reference to asteering system for a vehicle, the rotary-to-linear mechanism is notintended to be limited to such applications. It is contemplated that inaccordance with the exemplary embodiments, a rotary-to-linear conversionmechanism utilizing a pair of universal joints for isolating themechanism from misalignment and/or uneven loading can be applied to anyapplication.

In related embodiments, this system is related to the power assistsection, with the output being a linear motion, of any kind of steeringapplication. The power assist mechanism may be powered via a rotary typeelectric motor with potentially additional speed reducers, such as beltand pulley, gearbox, harmonic drive, etc., for torque multiplication,and the linear output is achieved by moving a shaft or linear section,such as a rack, along its axis. Between the power section and the linearoutput there may be a rotary-to-linear actuator (such as ballscrew,screw, ACME screw, rolling ring, etc.). It should be understood thatother types of appropriate speed reducers, shafts, and rotary-to-linearactuators not specifically described herein are also within the scope ofthis system.

As shown in FIG. 18, a mechanism 210 may include an interface B 212 thatmay connect the power section plus rotary-to-linear actuator 214 to thelinear section (e.g., rack) 216 such that the individual subcomponentsconstraints are all met. Thus, in a design phase of the mechanism 210,optimization of the mechanism 210 (in efficiency, size and durability)may be possible in the subcomponent level using the technology. This maysave time and have cost reductions in a manufacturing process, as thetechnology risk is minimized. For simplicity, the interface 212 may beprovided between the rotary-to-linear actuator 214 and the linearsection (e.g. rack) 216, as shown in FIG. 18.

It should be noted that while a rack is specifically described withrespect to this system, the mechanisms and systems described herein maybe incorporated into any rack based or drag link based system whereinthe ground may be the chassis, components that do not move, a suspensionsystem, or any other suitable components.

A characteristic of the interface B 212 described above may be toeliminate side loads (perpendicular to the axial direction of the linearmovement) and moments, which may be produced by geometric or dynamicmeans through external forces 218. Such conditions, if not avoided, maylead to undesirable friction increase.

In one embodiment of the mechanism 210, a ballscrew 220 may be used asthe rotary-to-linear actuator 214 and the linear section 216 may be arack. In this example, the ballscrew-screw 222 may rotate about the axis226 and the ballscrew-nut 224 may translate along the axis 226, as shownin FIG. 18. The nominal angle 228 between the two axes 226 and 230 isselected to be zero degrees, which would lead to the ball screw 222 andthe rack 216 being parallel. In actual applications, however, perfectlyparallel axes may be difficult to maintain, and therefore the axes 226,230 become skewed, as shown in an exaggerated skew, in FIG. 18. Inactuality, the skew is preferably not more than one or so degrees.Furthermore, in other embodiments, deviation from perfect conditions arestill within the scope of the embodiments. Special cases of the generalform of the actuator shown in FIG. 18 may be created such as if the twomentioned axes 226, 230 are parallel, the two mentioned axes 226, 230are collinear, or if side load effects (such as deflection of rack etc.)are negligible, or if the load could be acting in only one side of therack 216, or in various combinations of the above situations. It shouldalso be noted that the load may also act on the ballscrew-nut 224 or theball screw-screw 222.

In determining a properly constrained system (mechanism), the boundaryconditions may be set as follows: the ballscrew-screw 222 may turn aboutthe axis 226 (the A interface 232) but may not displace (thus, arevolute joint); the rack 216 may travel along the axis 230 and mayrotate about the axis 230 (thus, a cylindrical joint, even though thereare two cylindrical joints between the rack 216 and ground, it may becounted as one); and, the ballscrew-nut 224 may travel a lead lengthalong the axis 226 as long as when the ballscrew-screw 222 makes onerevolution the nut 224 does not rotate (with respect to axis 226). Itshould be understood that the basic kinematics of constrained rigidbodies includes many different types of pairs in spatial mechanisms,including spherical pairs, plane pairs, cylindrical airs, revolutepairs, prismatic pairs, and screw pairs, where each pair may define ajoint within a mechanical system. A cylindrical pair, or joint, keepstwo axes of two rigid bodies aligned, where the bodies will have anindependent translational motion along the axis and a relative rotarymotion around the axis. Therefore, a cylindrical pair removes fourdegrees of freedom from spatial mechanism, and the DOF=2. A revolutepair, or joint, keeps the axes of two rigid bodies together, where thebodies have an independent rotary motion around their common axis.Therefore, a revolute pair removes five degrees of freedom in spatialmechanism, and the DOF=1.

Interface B 212, shown in FIG. 18 between the ballscrew-nut 224 and therack 216, may be used to constrain the ballscrew-nut 224 properly (asdescribed in the third boundary condition described above). There areissues that need to be considered before an appropriate linkage isdesigned. It should be understood that an ideal joint has nothing butthe number of degrees of freedom that it should have, however, unlessthe joint is preloaded, a joint is always non-ideal since lash will addmore degrees of freedom. First, the tolerance of parts may force fornon-ideal joints and linkages, and, second, the loads may result incomponent deformation. As a result of these conditions, it may beassumed that the components are imperfect and that there will bepositional errors at any given instant but the imperfections areexpected to be small relative to the displacements and size of thecomponents. Thus, for all practical purposes the two axes 226, 230 maybe assumed to be slightly skew from this point on and that the sideloads on the rack 216 exist. Then, there may be a series of mechanismsthat may be correct based on kinematics (degree of freedom allows forone input) as well as dynamics. For a properly constrained system, theinterface B 212 may have three rotational degrees of freedom, while thesystem as a whole has one degree of freedom. In prior art systems, tocompensate for the irregularities between the axes 226, 230, the quickfix has usually been to provide rubber within a connection thatunder-constrains the system by providing too many degrees of freedom.Thus, the prior art mechanisms and systems are usuallyunder-constrained, that is, are provided with too many degrees offreedom and therefore not consistent in dynamic performance.

Turning now to FIG. 19, the ballscrew nut 224 is shown being loaded,through load 302, collinear to the ballscrew axis 226 at one side 304,which is a special case mechanism 300. However, even if load 302 is notperfectly collinear, the mechanism may still be within the scope ofthese embodiments. Thus, it may be possible to deviate the load 302 fromthe axis 226 a couple or so degrees. Combination joint 306 represents arevolute joint 272 at the rack cylindrical joint 244, which is possiblevia deflecting the joint. A calculation of the degrees of freedom“d.o.f.” is shown to equal one for the whole system, and thereforemechanism 300 is properly constrained. The d.o.f. may be calculatedusing the following equation:

d.o.f.=λ(L−J−1)+Σf_(i), wherein λ is the degree of the space, wherein 6degrees in the space means the system is operating in 3-dimensionalspace, L is the number of links in the system, J is number of joints inthe system, and f_(i) is the degree of freedom for each individual joint(for example, f_(i)=1 for revolute and slider joints, f_(i)=2 forcylindrical joints, f_(i)=3 for balljoints, etc.

For the FIG. 19 embodiment, the d.o.f. calculation is as follows:d.o.f.=λ(L−J−1)+Σf _(i)=1

-   -   λ=6    -   L=5    -   J=5    -   Σf_(i)=2 revolute+2 cylindrical+1 ball screw=2(1)+2(2)+(1)=7

For a d.o.f. calculation for the mechanism 300 of FIG. 19, it is notedthat the 5^(th) link is the 5^(th) joint. That is, the fifth link in theactuator is the bushing that forms the cylindrical joint 244. Thus, FIG.19 shows the collinear representation of the ballscrew 222 and nut 224and the force. The load previously acting at the end of the rack 216 (asin FIG. 18) is now a load 302 acting on the ballscrew nut 224. Thecylindrical joint 245 at the end of the ballscrew nut 224 is for dynamicloading concerns and kinematically not required, therefore thatparticular cylindrical joint 245 need not be included in the d.o.f.calculations. The cylindrical joint 245 at the end of the ballscrew nut224 is a redundant cylindrical joint 245 which should be collinear tothe ballscrew axis 226.

FIG. 20 shows a cross-sectional view of an implementation of themechanism 300 in an actuator 310. The “ground” or housing 312 is shownabout the mechanism 300. FIG. 21 shows an additional cross-sectionalview similar to FIG. 20, and revealing the ballscrew screw 222 withinthe revolute joint 272. FIGS. 22-24 show additional interior andexterior views of the mechanism 300 as housed within the special caseactuator.

FIG. 25 shows another embodiment of an interface between a movablelinear section (e.g. rack 216) and a rotary to linear actuator (e.g.,ballscrew screw 222 and ballscrew nut 424). This embodiment employs amechanism 420 that includes a “block on a plane” joint. A block on aplane joint has three degrees of freedom. A block may not separate fromthe plane to be considered a true block on a plane joint, and thereforeit may not “rock” relative to the plane. It may, however, slide relativeto the plane and spin. The block on a plane joint is used in thismechanism 420 by employing a ball nut 424 that has an angled face 440for sliding relative to a plane 436 that is connected to the rack 216such as through connector 442. Plane 436 thus moves with the rack 216.Side loads 426 and 428 are shown acting on rack 216, which come fromexternal forces such as from a wheel, suspension system, etc. The angleφ is similar to the angle 228 in FIG. 18, and represents an anglebetween the ballscrew screw axis 226 and the rack axis 230.

The angle between the ballscrew screw axis 226 and the plane 436, angleβ 430, will determine side load to the ballscrew screw 222. The block ona plane joint as used in this embodiment can center forces between theballscrew screw 222 and the ballscrew nut 424 about a center of theballscrew nut 424, without the need for fine adjustments. That is, aswill be further explained below, the rack 216 and the ballscrew nut 424are constrained from rotation about their axes, however, due toinevitable imperfections there may be slight rotation of these elements.The slight rotation actually serves to self-correct the interface bycentering the forces between the ballscrew screw 222 and the ballscrewnut 424 about a center of the ballscrew nut 424. This self-correctingaction eliminates the need for tedious, time-consuming fine adjustmentsbetween the elements during assembly.

If the angle β 430 between the ballscrew screw axis 226 and the plane436 is 90 degrees, then a separate anti-rotation for the ballscrew nut424, to prevent the ballscrew nut 424 from rotating, would be needed.Although the side load to the ballscrew screw 222 would be removed, theballscrew nut 424 would require an anti-rotation device. As can well beimagined, it β 430 was 90 degrees, then the ballscrew nut 424 wouldrotate relative to the plane 436, and therefore the rack 216 would notmove with the ballscrew nut 424. Thus, such an angle for β 430 is notdesirable. If the angle β 430 is 0 degrees, then the plane 436 would beparallel to the ballscrew screw axis 226, and the rack 216 will againnot move when the ballscrew nut 424 moves. The larger the deviation ofthe angle β 430 from 90 degrees, the larger the side load will be on theballscrew mechanism. It has been found that arranging the ballscrewscrew 222 to have an angle β 430 less than 90 degrees, but greater than81 degrees, works well with the mechanism 420. Manufacturers oftenspecify that the sideloads to the ballscrew mechanism be less than 10%of the axial load it carries. Thus, since 10% of 90 degrees is 9degrees, an appropriate angle for β 430 would be 81<β90. The closer to90 degrees β 430 is, the closer the ballscrew nut 424 is to rotating,and the further from 90 degrees β 430 is, the greater the side load ison the ballscrew mechanism. Thus, a compromise between possible rotationof the ballscrew nut 424 and side loads to the ballscrew mechanism maybe reached by selecting an angle of β 430 between 81 and 90 degrees. Itshould be understood that although 81 degrees is specified, in someinstances, if greater side loads than 10% of an axial load that aballscrew mechanism carries are acceptable, then β 430 may be less than81 degrees.

For the FIG. 25 embodiment, the actuator or mechanism 420 as a whole hasonly one degree of freedom, where the d.o.f. calculation is as follows:d.o.f.=λ(L−J−1)+ρf _(i)=1

-   -   λ=6    -   L=4    -   J=4    -   Σ f_(l)=1 revolute joint+1 cylindrical joint+1 ballscrew screw+1        block on plane=1(1)+1(2)+1(1)+1(3)=7

FIG. 26 shows an exterior view of the actuator housing for the mechanism420 described herein for providing a properly constrained interface. Thetie rods 422, motor 332, and the housing (ground) 312 are shown.

FIG. 27 shows a partial cross-sectional view of the mechanism 420,revealing the rack 216, the ballscrew screw 222, an the ballscrew nut424 and bolts 438 which may be employed to hold the plane 436 relativeto the ballscrew nut 424. FIG. 28 is another partial cross-sectionalview of the mechanism 420, similar to FIG. 27, but additionally exposinga cross-section of the revolute joint 272, and displaying the rack 216and ballscrew screw 222 within the ballscrew nut 424. FIG. 29 is anotherpartial cross-sectional view of the mechanism 420, similar to FIGS. 27and 28, but additionally showing the plane 436 that the ballscrew nut424 may abut against, and the angled face 440 of the ballscrew nut 424.FIG. 30 shows an enlarged view of the relevant area where the angledface 440 of the ballscrew nut 424 engages the plane 436.

It should be understood that there are alternative constructions of ablock on a plane, using a ballscrew nut 424 as the block, not disclosedherein that would also be within the scope of the mechanism 420. Forexemplary purposes only, the ballscrew nut 424 is shown as abuttingspacer element 434 which may include bearings (balls) 444 and the plane436 may include bearing surfaces 446 for engaging with the bearings 444.The bearing surfaces 446 may comprise a washer that is placed againstthe plane 436 for providing a hardened surface upon which the bearings444 can ride. It should be understood that the face 440 of the ballscrewnut 424 may additionally include a bearing surface such as a washer forproviding a hardened surface upon which the bearings 444 can ride. Thespacer element 434 may be a physical element that holds the bearings 444such as for proper spacing during assembly, or may simply be a spacebetween the face 440 (or bearing surface/washer on face 440) and thebearing surfaces 446. Also by example only, the plane 436 may beembodied within an angled plate-like extension that extends from aconnector 442 that connects the angled plate-like extension, plane 436,to the rack 216, as clearly shown in FIG. 31. The plane 436 may berigidly connected to the rack 216 such that the longitudinal motion ofthe rack 216 along its longitudinal axis 230 is translated to motion ofthe plane 436, in an equivalent direction. Except due to imperfections,the rack 216 and the ballscrew nut 424 do not rotate about their axes.The plane 436 may be held in place relative to the rack 216 using bolts438, which are further employed to maintain the ball nut 424 in placerelative to the plane 436. It should be understood that, in a block on aplane joint, the block may not depart from the plane, and thus is maynot rock relative to the plane. Thus, in the mechanism 420, theballscrew nut 424 is clamped to the plane 436 using bolts 438, and heldthereto with nuts 450, where the nuts 450 are threaded onto the shaftsof the bolts 438. The bolt heads 452 connect with the shafts of thebolts 438 and provide a means for tightening the bolts 438 and nuts 450.The shafts of the bolts 438 may travel through a flange 454 of theballscrew nut 424 so as not to interfere with the ballscrew nut424/ballscrew screw 222 operation. One side of the flange 454 has beendescribed as angled face 440. The other side of flange 454 is face 456which may be provided with a bearing surface, such as a washer, 458, forengaging with bearings 444 that abut a second plane 460. The secondplane 460 may have an angled face that is parallel with the angled facesof the first plane 436 and angled face 440. The planes 436 and 460 maybe apertured, that is, have an opening, to allow passage of theballscrew screw 222 therethrough. The opening of the plane 460 may belarger than the opening of the plane 436, since the opening of the plane460 may also be large enough to allow the passage of the ballscrew nut424 therethrough. Thus, it should be understood that the ballscrew nut424 is effectively “sandwiched” in between two plates (planes 436 and460) via bearings 444 and bearing surfaces. This sandwiching ensuresthat movement of the ballscrew nut 424 will translate to movement of therack 216, and movement of the rack 216 will translate to movement of theballscrew nut 424. That is, there is a lash free motion between theballscrew nut 424 and the rack 216. When the motor 332 operates torotate the ballscrew screw 222, the rotation of the ballscrew screw 222translates into longitudinal movement of the ballscrew nut 424.Depending on the direction of rotation of the ballscrew screw 222, theballscrew nut 424 will either push against the plane 436 or the plane460. Because the ballscrew nut 424 and planes 436, 460 are all clampedtogether, movement against either plane will cause a correspondingmovement to the rack 216 via the connector 442.

As shown in FIG. 31, it should further be understood that a similar“reversed” angle may be accomplished by angling the plane 436 away fromthe ball nut as it extends away from the rack 216, and having the face440 angled to complement the plane 436. The elements utilized in such anembodiment would otherwise be the same. FIG. 32 shows anothercross-sectional view of a potential configuration for the mechanism 420.

The previously described mechanisms and configurations may be achievedthrough deflecting components or joints appropriately along theparticular direction or twisting about an appropriate axis. The nextgeneration mechanization may eliminate the joints at interface B 212 inFIG. 18 and fill the interface B 212 with a flexible component that isattached in a fixed manner to both the rack 216 and to the ballscrew-nut224. Thus, for such a mechanism, gaps between components (or joints asthere are none), thus noise and vibration, the nonlinearity (incontrols) and number of components (reliability and assembly) may bereduced.

Turning to FIGS. 33-35, examples of mechanisms that use a flexiblecomponent may provide a compliant member adjacent the ballscrew nut asshown. That is, interface B 212 shown in FIG. 18 is replaced by aflexible member, such as rubber or deflectable strips. To prevent underconstrainment, a coupler as will be described may be used.

Enough degrees of freedom are achieved with the following mechanisms forapproximately matching kinematics. Turning now to FIG. 33, one exemplarycoupler 340 is shown which is suitable for use as the coupler 334 withinan actuator as previously described. The coupler 340 houses thecompliant member 324 at interface B 212 in FIG. 18. The coupler 340 mayinclude a first longitudinal opening 342 corresponding to the rack axis230 and a second longitudinal opening 344 corresponding to the ballscrewaxis 226. Although the coupler 340 may have one unitary body 346, thebody 346 may include a first body portion 348 for surrounding the rack216 and a second body portion 350 for surrounding the ballscrew nut 224.The unitary body 346 may be formed from a single, unjointed piece ofmaterial. A connecting portion 352 may be provided between the firstbody portion 348 and the second body portion 350 for appropriatelyspacing the coupler 340 about the rack 216 and the ballscrew nut 224.The second body portion 350 may further include a compliant member 324positioned within the second longitudinal opening 344.

Turning now to FIG. 34, another exemplary coupler 360 is shown. Thecoupler 360 may include a first longitudinal opening 362 correspondingto the rack axis 230 and a second longitudinal opening (hidden fromview) corresponding to the ballscrew axis 226. Although the coupler 360may have one unitary body 366, the body 366 may include a first bodyportion 368 for surrounding the rack 216 and a second body portion 370for surrounding the ballscrew nut 224. The unitary body 366 may beformed from a single, unjointed piece of material. The second bodyportion 370 may include a first end 372 having a U-shaped member 374,and a second end 376 having a ring shaped member 378. The ring shapedmember 378 and the U-shaped member 374 may be connected by strips 376which extend parallel to the longitudinal axis 226. The ballscrew nut224 may include a cylindrical shaped portion 380 nestled between thestrips 376 and a ring shaped portion 384 abutting the ring shaped member378. The strips 376 may pass through slots 382 in the ring shapedportion 384 of the ballscrew nut 224. The first body portion 368 and thesecond body portion 370 may be connected by a connecting portion 386. Inthe coupler 360, compliance may be achieved through deflecting materialof the strips 376. The compliance is met in three (up-down, side toside, and twisting) directions while maintaining axial rigidity. Thus,this embodiment achieves compliance without using rubber and withoutusing a jointed interface for the interface B 212.

Turning now to FIG. 35, another exemplary coupler 390 is shown. Thecoupler 390 may include a first longitudinal opening 392 correspondingto the rack axis 230 and a second longitudinal opening 394 correspondingto the ballscrew axis 226. Although the coupler 390 may have one unitarybody 396, the body 396 may include a first body portion 398 forsurrounding the rack 216 and a second body portion 400 for surroundingthe ballscrew nut 224. The unitary body 396 may be formed from a single,unjointed piece of material. The second body portion 400 may include afirst end 402 and a second end 404. Each end may include a main circularportion 406 with four smaller circular portions 408 evenly spaced aboutthe outer periphery of the main circular portion 406. Also for each end,a first C shaped portion 410 may surround an upper pair of circularportions 408 and a second C shaped portion 412 may surround a lower pairof circular portions 408. A first connecting strip 414 may connect thefirst C shaped portion 410 on the first end 402 to the first C shapedportion 410 on the second end 404. A second connecting strip 416 mayconnect the second C shaped portion 412 on the first end 402 to thesecond C shaped portion 412 on the second end 404. The ballscrew nut 224may be positioned between the main circular portions 406 and within thefirst and second connecting strips 414, 416. Compliance in the coupler390 may be achieved through deflecting material, such as in C-shapedportions 410, and first and second connecting strips 414, 416. Thus,compliance is met in three directions while maintaining axial rigidity.

Thus, in the above described couplers shown in FIGS. 33-35, only threedegrees of freedom are allowed for the interface (coupler) giving themechanism utilizing such a coupler a total of one degree of freedom, asin the prior embodiments, and thus such mechanisms are correctlyconstrained.

It should be understood that the interfaces described with respect tothe above embodiments, whether they be joints, joint combinations,linkages, and/or couplers, will most likely be non-ideal interfaces.Although ideal interfaces are preferred, such perfection is sometimesunrealistic. In any interface, the most degrees of freedom that it couldhave is six. In the embodiments described herein, the interfaces havebeen constrained to only have three degrees of freedom. The otherdegrees of freedom that have been eliminated may actually exist, even ifonly to a very small degree. Thus, it should be understood that ifmovement of a joint is enabled past a tolerance for that degree offreedom, then it may be counted as a degree of freedom. The tolerancemay be different depending on the type of movement for the degree offreedom and depending on the particular mechanism. For example only, ifa tolerance of movement in one direction is 0.75 mm, and if movement ofa joint in one direction is limited to no more than 0.5 mm, then thejoint may be seen as constrained in that direction, and therefore thatmovement would not qualify as a degree of freedom. If, however, thatsame joint is movable in that direction more than 0.75 mm, then it wouldbe considered to have a degree of freedom in that direction. In anotherexample, if the tolerance of twisting in one direction is one degree,then any joint that twists for less than one degree would be consideredconstrained in that direction. In most cases, movement of a joint in aconstrained direction, such as movement due to lash, is so negligiblethat the joint is easily recognizable as constrained in that direction,and therefore not a degree of freedom, and a joint having a degree offreedom in a particular direction is so obviously movable in thatdirection that it is easily recognizable as having a degree of freedomin that direction.

While the embodiments have been described with reference to exemplaryembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the embodiments. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the embodiments without departing fromthe essential scope thereof. Therefore, it is intended that theembodiments not be limited to the particular embodiment disclosed as thebest mode contemplated for carrying out these embodiments, but that theembodiments will include all embodiments falling within the scope of theappended claims. Moreover, the use of the terms first, second, etc. donot denote any order or importance, but rather the terms first, second,etc. are used to distinguish one element from another.

1. A steering system for a vehicle, comprising: a steering wheel beingpositioned for manipulation by a vehicle operator; a steering mechanismfor transmitting a steering operation of said steering wheel to vary theangular configuration of at least one wheel of said vehicle; a powerassist mechanism for providing an assisting force to said steeringmechanism, said power assist mechanism being activated in response tosaid steering operation of said steering wheel; and a load displacementsystem being operatively coupled to said power assist mechanism, saidload displacement system allowing transient loads of said steeringmechanism to be displaced.
 2. A steering system as in claim 1, whereinsaid power assist mechanism comprises: an electric motor for providing arotational force to a first motor pulley; a second motor pulley beingfixedly secured to a ball-screw; a ball-screw nut wherein saidball-screw is configured and dimensioned to meshingly engage saidball-screw nut; a first universal joint being fixedly attached on oneend to a rack housing, and said first universal joint being fixedlyattached to said electric motor on its opposing end; and a seconduniversal joint being fixedly attached to said rack on one end and beingfixedly attached to said ball-screw nut on its opposing end.
 3. Asteering system for a vehicle, comprising: a rack being movably mountedwithin a rack housing, said rack being coupled to a steerable roadwheel; a ball-screw mechanism being coupled to said rack at one end andan electric motor at the other, said electric motor providing anactuating force to said ball-screw mechanism, said actuating forcecausing said rack to move linearly within said rack housing; a firstcoupling mechanism coupling said electric motor to said rack housing;and a second coupling mechanism coupling a ball nut to said rack.
 4. Thesteering system as in claim 3, wherein said first coupling mechanism andsaid second coupling mechanism are first and second universal joints. 5.The steering system as in claim 4, wherein said actuating force is therotation of a first pulley fixedly secured to a rotatable shaft of saidmotor, said first pulley being coupled to a second pulley, said secondpulley being fixedly secured to a ball-screw screw of said ball-screwmechanism.
 6. The steering mechanism as in claim 4, wherein said firstand second universal joints each have a gimbal ring with a first pairand a second pair of pins for movably securing said gimbal ring, saidfirst pair of pins being orthogonal with respect to said second pair ofpins.
 7. The steering mechanism as in claim 4, wherein said firstuniversal joint movably secures said motor and its housing to said rackhousing.
 8. The steering mechanism as in claim 7, wherein said seconduniversal joint movably secures said ball-screw nut to said rack.
 9. Thesteering mechanism as in claim 4, wherein said ball-screw mechanismfurther includes a housing, said housing being secured movably securedto said second universal joint.
 10. The steering system as in claim 3,further comprising a plurality of sensors for providing signals to acontroller, said controller controlling the activation and deactivationof said electric motor.
 11. The steering system as in claim 10, whereinsaid plurality of sensors includes position sensors, force sensors,steering sensors, and a high-resolution sensor.
 12. The steering systemas in claim 3, wherein said rack includes an anti-rotation mechanism,said anti-rotation mechanism preventing the rotation of said rack. 13.The steering system as in claim 12, wherein said anti-rotation featureincludes a plurality of bearings and a protruding member being fixedlysecured to said rack, said plurality of bearings movably engaging anelongated opening of said rack housing.
 14. The steering system as inclaim 3, wherein said rack is movably coupled to a first road wheel andsaid steering system further comprises: a second rack being movablymounted within a second rack housing, said second rack being coupled toa second steerable road wheel; a second ball-screw mechanism beingcoupled to said second rack at one end and a second electric motor atthe other, said second electric motor providing an actuating force tosaid second ball-screw mechanism, said actuating force causing saidsecond rack to move linearly within said second rack housing; a firstcoupling mechanism coupling said second electric motor to said secondrack housing; and a second coupling mechanism coupling said second ballnut to said second rack, wherein said rack and said second rackindependently actuate said first road wheel and said second road wheel.15. The steering system as in claim 3, wherein said electric motorprovides a return torque for returning said rack to a center positioncorresponding to a center position of said road wheel.
 16. A method forproviding an actuation force to a rack of a vehicle, comprising:isolating non-axial loads from an electric motor of a steering system,said motor providing a rotational force to a rotatable member of arotary-to-linear conversion device; and isolating non-axial loads from alinearly actuatable member of said rotary-to-linear conversion device,said linearly actuatable member being coupled to a rack of said steeringsystem.
 17. A steering system for a vehicle, comprising: a rack beingmovably mounted within a rack housing, said rack being coupled to asteerable road wheel; a rotary-to-linear mechanism being coupled to saidrack at one end and an electric motor at the other, said electric motorproviding an actuating force to said rotary-to-linear mechanism, saidactuating force causing said rack to move linearly within said rackhousing; a first coupling mechanism coupling said electric motor to saidrack housing; and a second coupling mechanism coupling a ball nut tosaid rack.
 18. The steering system as in claim 17, wherein said firstcoupling mechanism and said second coupling mechanism are universaljoints.
 19. The steering system as in claim 17, wherein said firstcoupling mechanism and said second coupling mechanism are compliantmembers.